White light, real-time, scanning confocal microscopes have been used in clinical and investigative opthalmology for many years, and the applications of this technology to patients have expanded and include refractive surgery and use to assist in diagnosis of diseases. In clinical use, a camera can be attached to the confocal microscope, to record the images, and attached to a display device to display the images on a screen in real-time. The microscope and attached camera are generally stable and do not move. However, the eye being observed through the confocal microscope by the ophthalmologist is not necessarily stable or stationary. The subject's eye may move due to the inability of the subject to maintain a totally steady gaze, or due to movements of the subject causing the subject's eyes to move in the observed field. Additionally, portions of the eye being observed can move due to intrinsic biological factors, such as involuntary movements. Such movements may be non-linear in the sense that a movement in one area of the observed field may not be reflected in another area of the observed field. The movement may be localized to a portion of the observed field and other movements reflected in another area of the observed field. These types of movements make the interpretation of the observed images difficult.
In the confocal microscope system, the camera and microscope are stabilized with minimal movements, but the observed eye is constantly moving. Even “minor” movements can become a significant problem as the microscope will magnify the image of the movement. At magnification levels of around 500× that is needed to visualize cellular level details within the eye, it is apparent that a minor eye movement can prevent significant visualization difficulties to the ophthalmologist trying to observe the non-linear moving image field.
Image stabilization has been addressed in the prior art from the standpoint of stabilization of camera movement (such as in hand held video recorders) to prevent a blurring or movement in the imaged field. Additionally, stabilization of cameras on moving platforms observing a relatively still object has been addressed. However, stabilization of the imaged field to account for undesired movement of the imaged subject, particularly a non-linear type of movement, has not been examined and stabilization in this sense presents added difficulties. Non-linear movement is used in the sense that movement in one portion of the observed field may not reflect movement in another portion of the observed field. Prior art stabilization techniques generally apply a global shift or translation of the image, that is, each portion of the image receives the same “correction.” With non-linear movement of the subject in the observed or imaged field, global corrections are insufficient to effect image stabilization. A technique is needed to identify and quantify changing areas of an image, and to correct those areas of the image to account for the changes.